From France, I’ve been barely exposed to Heathcliff… Except for a random animated series from the 80s starring him and a bunch of other OC cats. And I wouldn’t have recognized the name later, because they’d changed it for the French localization (they called him “Isidore”).
I’ve only learned about Heathcliff (and the fact the cartoon was supposed to be partly based on him) when I watched a Quinton Reviews video on youtube. The whole video was based on the joke that Quinton was basically an authority on Garfield material at that point and he reviewed Heathcliff as “Garfield but worse” (maybe).